Catheters are used in numerous medical procedures. In particular, catheters are used for the introduction or removal of fluids from various venous regions and vessels throughout the body, such as for hemodialysis. The procedure by which these catheters are introduced to the body is delicate and complex. One particularly intricate challenge to catheterization is enlarging a hole in the flesh and vessel to be catheterized while minimizing blood loss and trauma to the patient.
Generally, to insert any catheter in a blood vessel, the vessel is identified by aspiration with a long hollow needle in accordance with the Seldinger technique. When blood enters a syringe attached to the needle, indicating that the vessel has been found, a thin guide wire is then introduced, typically through the syringe needle or other introducer device, into the interior of the vessel. The introducer device is then removed, leaving the guide wire within the vessel. The guide wire projects beyond the surface of the skin.
At this point, several options are available to a physician for catheter placement. The simplest option is to pass a catheter into the vessel directly over the guide wire. The guide wire is then removed. However, use of this technique is only possible in cases where the catheter is of a relatively small diameter, made of a stiff material and not significantly larger than the guide wire. If, however, the catheter is of a relatively large diameter and/or not made of a soft material, one preferable method of inserting the catheter into the vessel is through an introducer sheath. The introducer sheath is simply a large, stiff, thin-walled tube, which serves as a temporary conduit for the catheter that is being placed. The sheath is positioned by placing a dilator, which has a hollow passageway along its longitudinal axis, inside of the sheath and passing both the dilator and the sheath together into the vessel over the guide wire. The dilator expands the opening in the blood vessel to allow for catheter insertion into the vessel. The guide wire and dilator are then removed, leaving the thin-walled sheath in place. The catheter is then inserted into the vessel through the sheath.
In a setting where a catheter with a hub or other attachment at the proximal end of the catheter has a feature which is larger than that of the inner diameter of the sheath, it is necessary to have a tear-away sheath that can be split away from the catheter as the sheath is being removed from the patient. By splitting the sheath along its longitudinal axis as the sheath is being removed from the patient, the inserting physician will be able to pull out the sheath in such a way that the portion removed from the patient is split, thereby not interfering with any encumbrances on the catheter. Generally, tear away sheaths are manufactured in a way that aids in the tearing of the sheath at two opposing points on the circumference of the sheath, thereby splitting the sheath into two halves separated longitudinally through the center of the sheath.
A sheath is generally constructed with a hub at its proximal end. This hub serves as a handle, a mating point for a dilator, and a flat surface to aid in the prevention of blood loss or contamination. When a sheath needs to be split apart in order to be successfully withdrawn from the body while leaving the catheter in place, the hub will also have to be split apart in order to clear the catheter. Preferably, the hub will split along the same lines as the sheath. To accomplish this, the hub must be designed with reveals or other weaknesses along two longitudinal lines aligned with the weaknesses in the sheath. Some previous examples of these weaknesses are tabs or webs which connect two halves of the hub, or recesses in the material comprising the hub. The weaknesses in the hub will help the inserting physician to break apart the hub in line with the tear seams on the sheath.
Another important facet of the hub is a set of tabs that protrude from the center. These tabs not only help the inserting physician to align, insert and withdraw the sheath, but also to pull the sheath so that the sheath can be removed from around a catheter while still leaving the catheter in place. There are a number of different tab configurations, but it is important to have one which allows for easy maneuverability, control, and leverage. One design includes a hub wherein the tabs protrude from the hub perpendicular to a plane which includes the tear seams in the sheath and the longitudinal axis of the sheath. In this design, the tabs are diametrically opposed from each other and are spaced in such a way that when the tabs are grasped and pulled apart from each other, the sheath and its hub will split down the middle. Another desirable feature of the tabs is that the tabs provide leverage for breaking apart the hub in a manner that does not cause trauma to the incision in the body.
During insertion, especially in the time between the removal of the dilator from the sheath and the insertion of the catheter through the sheath, it is possible for blood loss through the sheath, or the introduction of contaminants or air through the sheath and into the vessel. For this reason, it is desirable that measures be taken to prevent blood, air or contaminants from traveling through the sheath. In the past, inserting physicians have simply held their thumb over the opening in the proximal end of the sheath; however, a more permanent and reliable means for preventing blood, air or contaminants from traveling through the sheath is desirable. It is therefore desirable for the hub to include a valve located in the sheath. Such a valve would facilitate the insertion of objects such as a catheter, dilator or syringe through the sheath while restricting blood loss and reducing the chance of contaminants entering the patient's bloodstream when the sheath is not engaged with a dilator or a catheter.
In the case where a sheath does not have a small diameter or a narrow point, the dilator is often used to aid in the insertion of the sheath. The dilator has a long tubular section, the outside diameter of which is slightly smaller than the inside diameter of the sheath. The dilator also has a pointed tip on its distal end and a hollow center, which runs along the entire length of the dilator. The dilator is inserted into the body with the guidewire running through its center, thereby allowing the tip of the dilator to follow the guidewire to the place that is to be catheterized. On its proximal end, the dilator may have a hub. Like the hub of the sheath, this hub can also serve a number of purposes, such as providing a stable handle to aid in guiding the dilator into the vein, and as a mechanism which can mate with the sheath hub to form a locked connection.
Some dilator and sheath assemblies that include a connection between the dilator and sheath are known. U.S. Pat. No. 5,885,217 to Gisselberg et al. discloses a dilator and sheath assembly, wherein the dilator and sheath are held together by locking tabs which provide a stop to hold the dilator in place during insertion. However, in this configuration, the dilator may rotate about its longitudinal axis in relation to the sheath, thereby inadvertently and prematurely disengaging the dilator from the sheath. U.S. Pat. No. 5,098,392 to Fleischhacker et al. discloses a dilator and sheath assembly, wherein the dilator is attached to the sheath through a clamp wherein the clamp is part of the dilator hub. However, this design presents the ability to come unclamped leading to the dilator backing out of the sheath. U.S. Pat. No. 4,772,266 to Groshong discloses a dilator and sheath assembly, wherein the hubs of the dilator and the sheath lock together by means of compression. However, it would be possible for the dilator to back out of the sheath in this configuration if excessive force is exerted on the tip of the dilator.
It would be beneficial to provide a dilator and sheath assembly that incorporates a stable releasably locking mechanism to prevent the dilator from backing out of the sheath longitudinally during insertion which is not prone to coming unlocked or releasing during use. It would also be beneficial for the sheath of the dilator and sheath assembly to have a means for sealing the passageway to the patient's vessel, thereby restricting blood loss and reducing the introduction of contaminants into the bloodstream. Moreover, it would be beneficial for this type of mechanism to have handles, which allow the inserting physician to gain leverage in the process of splitting the sheath apart.